Mutagenicity of benzidine and benzidine-congener dyes and selected monoazo dyes in a modified Salmonella assay

We have evaluated the mutagenic activity of a series of diazo compounds derived from benzidine and its congeners o-tolidine, o-dianisidine and 3,3'-dichlorobenzidine as well as several monoazo compounds. The test system used was a modification of the standard Ames Salmonella assay in which FMN, hamster liver S9 and a preincubation step are used to facilitate azo reduction and detection of the resulting mutagenic aromatic amines. All of the benzidine and o-tolidine dyes tested were clearly mutagenic. The o-dianisidine dyes except for Direct Blue 218 were also mutagenic. Direct Blue 218 is a copper complex of the mutagenic o-dianisidine dye Direct Blue 15. Pigment Yellow 12, which is derived from 3,3'-dichlorobenzidine, could not be detected as mutagenic, presumably because of its lack of solubility in the test reaction mixture. Of the monoazo dyes tested, methyl orange was clearly mutagenic, while C.I. Acid Red 26 and Acid Dye (C.I. 16155; often referred to as Ponceau 3R) had marginal to weak mutagenic activity. Several commercial dye samples had greater mutagenic activity with the modified test protocol than did equimolar quantities of their mutagenic aromatic amine reduction products. Investigation of this phenomenon for Direct Black 38 and trypan blue showed that it was due to the presence of mutagenic impurities in these samples. The modified method used appears to be suitable for testing the mutagenicity of azo dyes, and it may also be useful for monitoring the presence of mutagenic or potentially carcinogenic impurities in otherwise nonmutagenic azo dyes.     

Developing azo and formazan dyes based on environmental considerations: Salmonella mutagenicity

In previous papers, the synthesis and chemical properties of iron-complexed azo and formazan dyes were reported. It was shown that in certain cases iron could be substituted for the traditionally used metals such as chromium and cobalt, without having an adverse effect on dye stability. While these results suggested that the iron analogs were potential replacements for the commercially used chromium and cobalt prototypes, characterization of potentially adverse environmental effects of the new dyes was deemed an essential step in their further development. The present paper provides results from using the Salmonella/mammalian microsome assay to determine the mutagenicity of some important commercial metal complexed dyes, their unmetallized forms, and the corresponding iron-complexed analogs. The study compared the mutagenic properties of six unmetallized azo dyes, six commercial cobalt- or chromium-complexed azo dyes, six iron-complexed azo dyes, six unmetallized formazan dyes, and six iron-complexed formazan dyes. The results of this study suggest that the mutagenicity of the unmetallized dye precursors plays a role in determining the mutagenicity of the iron-complexes. For the monoazo dye containing a nitro group, metal complex formation using iron or chromium decreased or removed mutagenicity in TA100; however, little reduction in mutagenicity was noted in TA98. For the formazan dye containing a nitro group, metal-complex formation using iron increased mutagenicity. Results varied for metal-complexes of azo and formazan dyes without nitro groups, but in general, the metal-complexed dyes based on mutagenic ligands were also mutagenic, while those dyes based on nonmutagenic ligands were nonmutagenic.     

Reduction and partial degradation mechanisms of naphthylaminesulfonic azo dye amaranth by <Emphasis Type="Italic">Shewanella decolorationis</Emphasis> S12

Reduction and biodegradation mechanisms of naphthylaminesulfonic azo dye amaranth using a newly isolated Shewanella decolorationis strain S12 were investigated. Under anaerobic conditions, amaranth was reduced by strain S12, and a stoichiometric amount of two reduction products RP-1 and RP-2 were generated. UV/visible spectrophotometric and high performance liquid chromatography (HPLC) analysis indicated that RP-1 and RP-2 were 1-aminenaphthylene -4-sulfonic acid and 1-aminenaphthylene-2-hydroxy-3, 6-disulfonic acid. The result strongly supports a mechanism of azo dye reduction by the process via the reductive cleavage of the azo bond to form corresponding aromatic amines. The result of HPLC analyses revealed that these aromatic amines were not able to be mineralized by strain S12 under anaerobic conditions. But after re-aeration of the decolorized culture, RP-2 was mineralized completely by this microorganism, but the consumption of RP-1 was not observed. Ames test showed that amaranth had mutagenic but no cytotoxic potential. The mutagenic potential was relieved after the anaerobic treatment with strain S12 as the mutagenic effect of the two reduction products from amaranth was not detected by Ames test. Thus, the ability of strain S12 to reduce and partially mineralize the naphthylaminesulfonic azo dye efficiently was demonstrated, which can potentially be used to biodegrade and detoxify wastewater containing azo dyes using an alternating anaerobic/aerobic treatment procedure.     

Azo reduction of trypan blue to a known carcinogen by a cell-free extract of a human intestinal anaerobe.

The azo reductase activity of a cell-free extract of Fusobacterium sp. 2 is characterized using trypan blue as a substrate. Either chemical reduction of this dye with sodium hydrosulfite or reduction by the cell-free extract produces a mutagenic product, o-tolidine. The o-tolidine is mutagenic in the Ames Salmonella/mammalian-microsome mutagenicity test when activated by a rat liver S9 preparation.     

Mutagenicity test of dyes used in cosmetics with the Salmonella/mammalian-microsome test.

37 dyes including 3 anthraquinone, 22 azo; 5 xanthene, 5 fluorandiol, and 2 thioindigo dyes, were tested for mutagenic potential with the Salmonella/mammalian-microsome test. Two frame-shift histidine mutants (TA1537 and TA98) and two base-pair substituted histidine mutants (TA1535 and TA100) of Salmonella typhimurium were employed. Both the spot test and the plate-incorporation assay indicated that one azo dye, D&C Orange No. 17, was mutagenic with three of the bacterial test strains. The mutagenic response of D&C Orange No. 17 was depressed by the addition of the microsomal fractions from rat livers. Of the chemicals used to synthesize D&C Orange No; 17 was depressed by the addition of the microsomal fractions from rat livers. Of the chemicals used to synthesize D&C Orange No. 17, beta-naphthol was not mutagenic but 2,4-dinitroaniline was mutagenic to the same Salmonella strains as D&C Orange No. 17 . Dimethyl sulfoxide extracts of lipsticks of similar formula but without D&C Orange No. 17 were tested in the plate incorporation assay. Only those containing D&C Orange No. 17 were mutagenic and the dye was mutagenic at concentrations consumed in normal daily use.     

Release of mutagens from finished leather

Extracts of a leather widely used in the furniture and dress-making industries were tested for their mutagenic activity in the Salmonella/microsome assay. Extracts obtained after vigorous treatment of leather samples in a Soxhlet apparatus with toluene or ethanol were mutagenic in strain TA98 of S. typhimurium in the absence of S9 mix. The analysis of extracts of leather at various intermediate stages of processing showed that the mutagenic activity appeared after the coloration process. The responsible compound was identified to be an azo dye (Color Index: Acid Brown 83) whose mutagenic potency was about 4 revertants/micrograms.     

Evaluation of the Presence of Mutagenic Dyes in Sediments from Cristais River

Azo dyes are largely used by coloring textiles and can contaminate the aquatic environment, including the sediment, through their release through effluent discharges. In this work the presence of mutagenic azo dyes was evaluated using Thin Layer Chromatography in sediment samples of the Cristais River upstream and downstream of an azo dye processing plant discharge area. Mutagenicity of the sediment samples was also analyzed using the Salmonella/microsome assay with the strain YG1041 in the presence and absence of S9. Extracts of benthic organisms collected in the same area were analyzed for the presence of dyes. The dyes CI Disperse Blue 373 and CI Disperse Orange 37 as well as three unknown fluorescent compounds were detected only in the sediment samples collected downstream of the industrial discharge. Activity was detected with the Salmonella assay in the three samples analyzed but higher values were obtained after the azo dye processing plant when compared to the reference site. This effect could be partially explained by the presence of the mutagenic dyes detected, considering their mutagenic potencies. No dyes were found in the extracts of the organisms. Further studies should be performed to evaluate the fate and effects of these dyes in the sediment and in the aquatic community and their potential to be transferred to the water column.     

Microarray method to monitor 40 intestinal bacterial species in the study of azo dye reduction

Azo dyes are widely used in dye manufacturing, paper printing, textile industries, and as tattoo pigmentation. Since intestinal and skin bacteria can metabolize certain azo dyes to carcinogenic compounds, many researchers have studied the azoreductases of these bacteria. In this study, we used a microarray method to identify the intestinal bacterial species from cultured fecal samples in Brain Heart Infusion (BHI) broth with or without azo dyes that may be involved in azo dye reduction. The microarray was designed to identify 40 bacterial species that are reported in the literature to be predominant in human feces. Results from this study showed 26-30 species are present in the cultured fecal samples. The representative bacteria were then examined for the azo dye reduction activity.     

氧气对混合菌群脱色降解偶氮染料效果的影响

【背景】偶氮染料及其中间产物具有一定的环境毒性,利用混合菌群降解偶氮染料是一种环境友好型方法,但降解过程中氧气的存在起到至关重要的作用,可以促进或抑制偶氮染料的微生物降解作用。【目的】探讨氧气对偶氮染料微生物脱色液的影响,分析氧气对混合菌群脱色降解偶氮染料效果的影响。【方法】利用混合菌群DDMY1在3种培养条件(好氧、厌氧、兼氧)下,对7种偶氮染料进行脱色降解,探讨偶氮染料脱色液对氧气的响应情况,利用紫外可见分光光度法(ultraviolet visible spectrophotometry,UV-vis)和傅里叶变换红外光谱法(Fourier transform infrared spectroscopy,FTIR)对脱色产物进行分析。【结果】在兼氧和厌氧条件下反应48 h后的染料脱色液,与氧气充分接触后,部分偶氮染料微生物脱色液发生较为明显的复色现象,如活性黑5、直接黑38;UV-vis分析结果表明,这种复色现象是由于脱色液与氧气接触之后产生新物质所致;FTIR分析结果表明,混合菌群对发生复色反应的偶氮染料仍然具有一定脱色降解效果,但是脱色尚不够完全。【结论】兼氧和厌氧条件下,氧气对部分偶氮染料微生物脱色液具有较为明显的影响,从而影响混合菌群对偶氮染料的整体脱色效果,这可为今后研究偶氮染料彻底生物降解提供理论基础。     

Evaluation of azo food dyes for mutagenicity and inhibition of mutagenicity by methods using Salmonella typhimurium

The mutagenicity of 4 azo dyes (FD&C Yellow No. 5, FD&C Yellow No. 6, FD&C Red No. 40 and amaranth) that are widely used to color food has been evaluated. 4 different methods were used: (1) the standard Ames plate-incorporation assay performed directly on the dyes in the absence of S9 and in the presence of rat- or hamster-liver S9; (2) application of the standard plate assay to ether extracts of aqueous solutions of the dyes; (3) a variant of the standard assay, using hamster liver S9, preincubation, flavin mononucleotide (FMN) and other modifications designed to facilitate azo reduction; and (4) reduction of the dyes with sodium dithionite, followed by ether extraction and the standard plate assay. Assays that include chemical reduction (methods 3 and 4) were included because azo compounds ingested orally are reduced in the intestine with the release of free aromatic amines. No mutagenic activity was seen for any of the azo dyes tested by using the standard Ames plate assay (method 1). Ether extracts of some samples of FD&C Yellow No. 6, FD&C Red No. 40 and amaranth were active (method 2), but only at high doses, generally 250 mg-equivalents or more per plate. These results indicate the presence of low levels of ether-extractable mutagenic impurities. The FMN preincubation assay (method 3) gave negative results for all dye samples tested. Most batches of FD&C Red No. 40 tested had mutagenic activity that was detectable when the ether extract of less than 1 mg of dithionite-reduced dye was plated in the presence of S9 (method 4). This finding implies that an impurity in these samples of FD&C Red No. 40 can be reduced to yield an ether-extractable mutagen. Dithionite-reduced samples of FD&C Yellow No. 6 and amaranth showed ether-extractable mutagenic activity only at much higher doses than those at which activity was seen with most dithionite-reduced samples of FD&C Red No. 40 (method 4). FD&C Yellow No. 5 showed no mutagenic activity with this method. Mutagenic activity was not detected when FD&C Red No. 40 was tested by using the azo reduction preincubation assay with FMN (method 3).(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of new 2,2'-dimethyl-5,5'-dipropoxybenzidine- and 3,3'-dipropoxybenzidine-based direct dye analogs for mutagenic activity by use of the Salmonella/mammalian mutagenicity assay

As part of a continuing study aimed at establishing structure-activity relationships and heuristic principles useful for the design of non-genotoxic azo dyes, a series of new direct dyes based on two non-mutagenic benzidine analogs, 2,2'-dimethyl-5,5'-dipropoxybenzidine and 3,3'-dipropoxybenzidine, were evaluated for mutagenic activity in Salmonella typhimurium strains TA98 and TA100. These strains are widely used for mutagenicity screening and have been shown to detect the mutagenic activity of benzidine analogs. While some toxicity was seen with some dyes at high doses, all of the dyes examined were judged non-mutagenic with and without metabolic activation in the standard Salmonella plate-incorporation assay. The results in the standard test are consistent with the properties of the diamines themselves. However, only one of the dyes was non-mutagenic when a reductive-metabolism pre-incubation assay was used. The results of this study suggest that although benzidine analogs are potential replacements for benzidine, there is a need to understand which mutagenic products are produced when reductive metabolism is present. There is also a need to know whether or not metal complexes of these dyes are mutagenic. Such information will allow the development of new non-mutagenic azo dyes.     

Degradation of Remazol Red dye by <Emphasis Type="Italic">Galactomyces geotrichum</Emphasis> MTCC 1360 leading to increased iron uptake in <Emphasis Type="Italic">Sorghum vulgare</Emphasis> and <Emphasis Type="Italic">Phaseolus mungo</Emphasis> from soil

Removal of azo dyes from the effluent generated by textile industries is rather difficult. Azo dyes represent a major class of synthetic colorants that are both mutagenic and carcinogenic. Galactomyces geotrichum MTCC 1360, a yeast species, showed more than 96% decolorization of the azo dye Remazol Red (50 mg/L) within 36 h at 30°C and pH 11.0 under static condition with a significant reduction in the chemical oxygen demand (62%) and total organic carbon (41%). Peptone (5.0 g/L), rice husk (10 g/L extract), and ammonium chloride (5.0 g/L) were found to be more significant among the carbon and nitrogen sources used. The presence of tyrosinase, NADH-DCIP reductase, riboflavin reductase and induction in azo reductase and laccase activity during decolorization indicated their role in degradation. High performance thin layer chromatography analysis revealed the degradation of Remazol Red into different metabolites. Fourier transform infrared spectroscopy and high performance liquid chromatography analysis of samples before and after decolorization confirmed the biotransformation of dye. Atomic absorption spectroscopy analysis revealed a less toxic effect of the metabolites on iron uptake by Sorghum vulgare and Phaseolus mungo than Remazol Red dye. Remazol Red showed an inhibitory effect on iron uptake by chelation and an immobilization of iron, whereas its metabolites showed no chelation as well as immobilization of iron. Phytotoxicity study indicated the conversion of complex dye molecules into simpler oxidizable products which had a less toxic nature.     

Comparison of 7 azo dyes and their azo reduction products in the rat and hamster hepatocyte primary culture/DNA-repair assays

Pursuant to the characterization of species differences in the effects of chemical carcinogens, several studies have demonstrated that hamster hepatocytes are more effective than rat hepatocytes in mediating the metabolic activation of certain chemicals to their genotoxic (i.e., mutagenic) derivatives. In the present investigation, a comparison of the amount of DNA repair induced in rat and hamster hepatocytes by 7 azo dyes and 7 aromatic amine azo reduction products of the dyes was performed using the primary hepatocyte culture/DNA repair (HPC/DR) assay. Congo Red and its azo reduction product, benzidine, were more potent inducers of DNA repair in hamster than in rat hepatocytes, whereas Trypan Blue and its reduction product, o-tolidine, were equipotent in the 2 hepatocyte systems. Evans Blue, another o-tolidine-based dye, elicited a greater DNA-repair response in hamster hepatocytes. The absolute potency of these dyes, however, was much less than their reduction products. o-Aminoazotoluene was the most potent of the dyes tested, and its DNA repair-inducing activity was much greater than that of its azo reduction products, o-toluidine and 2,5-diaminotoluene. Ponceau SX, which is carcinogenic in hamsters, but not in rats, was inactive in both hepatocyte systems. Dimethylaminobenzeneazo-1-naphthalene and its 2-naphthalene congener, as well as the 1- and 2-naphthylamine azo reduction products of these dyes, were more potent in hamster than in rat hepatocytes. However, the DNA repair-inducing activities of the parent dyes could not be entirely accounted for by the potencies of their respective naphthylamine derivatives. Taken together, these findings extend previous observations of the superior metabolic activation capabilities of hamster, relative to rat hepatocytes, and further demonstrate the utility of testing chemicals in both the hamster and rat HPC/DR assays.     

Degradation of azo compounds by ligninase from Phanerochaete chrysosporium: involvement of veratryl alcohol

Phanerochaete chrysosporium decolorized several polyaromatic azo dyes in ligninolytic culture. The oxidation rates of individual dyes depended on their structures. Veratryl alcohol stimulated azo dye oxidation by pure lignin peroxidase (ligninase, LiP) in vitro. Accumulation of compound II of lignin peroxidase, an oxidized form of the enzyme, was observed after short incubations with these azo substrates. When veratryl alcohol was also present, only the native form of lignin peroxidase was observed. Azo dyes acted as inhibitors of veratryl alcohol oxidation. After an azo dye had been degraded, the oxidation rates of veratryl alcohol recovered, confirming that these two compounds competed for ligninase during the catalytic cycle. Veratryl alcohol acts as a third substrate (with H2O2 and the azo dye) in the lignin peroxidase cycle during oxidations of azo dyes.     

Distinguishing potential sources of genotoxic exposure via HPRT mutations

We utilize T-cell HPRT mutations to monitor exposure to environmental mutagens in siblings of children who have developed cancer at a persistently high rate in Toms River, New Jersey, U.S.A. A preliminary epidemiological study has found a statistically-significant association between drinking public water (by pregnant mother or infant) and subsequent risk for childhood cancer. Three potential sources of mutagenic exposures in Toms River may have increased the rate of carcinogenic initiation significantly in children: 1. Benzidine-based, other azo dye and anthraquinone dye wastes released by Ciba-Geigy, 2. Styrene-acrylonitrile (SAN) trimer and other plastic wastes of Union Carbide, and 3. Radium-224, present in unusually high concentrations in the Cohansey aquifer. Specific patterns of HPRT mutations are utilized to distinguish these various potential sources of carcinogenic exposures in the drinking water of families with childhood cancer and to differentiate chemically or radiologically induced cancers from those which occur spontaneously.     

Influence of aromatic substitution patterns on azo dye degradability by Streptomyces spp. and Phanerochaete chrysosporium.

Twenty-two azo dyes were used to study the influence of substituents on azo dye biodegradability and to explore the possibility of enhancing the biodegradabilities of azo dyes without affecting their properties as dyes by changing their chemical structures. Streptomyces spp. and Phanerochaete chrysosporium were used in the study. None of the actinomycetes (Streptomyces rochei A10, Streptomyces chromofuscus A11, Streptomyces diastaticus A12, S. diastaticus A13, and S. rochei A14) degraded the commercially available Acid Yellow 9. Decolorization of monosulfonated mono azo dye derivatives of azobenzene by the Streptomyces spp. was observed with five azo dyes having the common structural pattern of a hydroxy group in the para position relative to the azo linkage and at least one methoxy and/or one alkyl group in an ortho position relative to the hydroxy group. The fungus P. chrysosporium attacked Acid Yellow 9 to some extent and extensively decolorized several azo dyes. A different pattern was seen for three mono azo dye derivatives of naphthol. Streptomyces spp. decolorized Orange I but not Acid Orange 12 or Orange II. P. chrysosporium, though able to transform these three azo dyes, decolorized Acid Orange 12 and Orange II more effectively than Orange I. A correlation was observed between the rate of decolorization of dyes by Streptomyces spp. and the rate of oxidative decolorization of dyes by a commercial preparation of horseradish peroxidase type II, extracellular peroxidase preparations of S. chromofuscus A11, or Mn(II) peroxidase from P. chrysosporium. Ligninase of P. chrysosporium showed a dye specificity different from that of the other oxidative enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of aromatic substitution patterns on azo dye degradability by Streptomyces spp. and Phanerochaete chrysosporium.

Twenty-two azo dyes were used to study the influence of substituents on azo dye biodegradability and to explore the possibility of enhancing the biodegradabilities of azo dyes without affecting their properties as dyes by changing their chemical structures. Streptomyces spp. and Phanerochaete chrysosporium were used in the study. None of the actinomycetes (Streptomyces rochei A10, Streptomyces chromofuscus A11, Streptomyces diastaticus A12, S. diastaticus A13, and S. rochei A14) degraded the commercially available Acid Yellow 9. Decolorization of monosulfonated mono azo dye derivatives of azobenzene by the Streptomyces spp. was observed with five azo dyes having the common structural pattern of a hydroxy group in the para position relative to the azo linkage and at least one methoxy and/or one alkyl group in an ortho position relative to the hydroxy group. The fungus P. chrysosporium attacked Acid Yellow 9 to some extent and extensively decolorized several azo dyes. A different pattern was seen for three mono azo dye derivatives of naphthol. Streptomyces spp. decolorized Orange I but not Acid Orange 12 or Orange II. P. chrysosporium, though able to transform these three azo dyes, decolorized Acid Orange 12 and Orange II more effectively than Orange I. A correlation was observed between the rate of decolorization of dyes by Streptomyces spp. and the rate of oxidative decolorization of dyes by a commercial preparation of horseradish peroxidase type II, extracellular peroxidase preparations of S. chromofuscus A11, or Mn(II) peroxidase from P. chrysosporium. Ligninase of P. chrysosporium showed a dye specificity different from that of the other oxidative enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

3-Methoxy-4-aminoazobenzene, a unique carcinogenic aromatic amine as a substrate for cytochrome-P-450-mediated mutagenesis

Rat liver microsomal enzyme(s) that catalyze mutagenic activation of a carcinogenic aminoazo dye, 3-methoxy-4-aminoazobenzene (3-MeO-AAB), was studied by virtue of the Salmonella typhimurium TA98 assay using o-aminoazotoluene (OAT) as the control. Male Wistar rats were pretreated with phenobarbital (PB), 3-methylcholanthrene (MC) or polychlorinated biphenyl (PCB), and the liver microsomal activities for mutagenic activation of 3-MeO-AAB and OAT were examined. In agreement with the reported results on several carcinogenic aromatic amines, MC pretreatment resulted in greater activation of microsomal activity in the OAT mutagenesis (about a 4-fold increase as compared to the untreated control) than did PB (1.5-fold increase). By contrast, the mutagenic activation of 3-MeO-AAB is found to be more efficiently catalyzed by those enzyme(s) that are induced by PB pretreatment (4-fold increase) than by those that are induced by MC (1.8-fold increase). The induced enzymes that principally mediate the mutagenic activation of these azo dyes are indicated to be cytochrome P-450s, because the mutagenic activation was strongly inhibited by addition of cytochrome P-450 inhibitors such as 2-diethylaminoethyl-2,2-diphenylvalerate (SKF 525A) and 7,8-benzoflavone. These data suggest that 3-MeO-AAB is a unique carcinogenic aromatic amine as a substrate for mutagenic activation via catalysis of those cytochrome P-450s that are induced by PB pretreatment.     

Purification and identification of an FMN-dependent NAD(P)H azoreductase from Enterococcus faecalis

Azoreductases reduce the azo bond (N=N) in azo dyes to produce colorless amine products. Crude cell extracts from Enterococcus faecalis have been shown to utilize both NADH and NADPH as electron donors for azo dye reduction. An azoreductase was purified from E. faecalis by hydrophobic, anion exchange and affinity chromatography. The azoreductase activity of the purified preparation was tested on a polyacrylamide gel after electrophoresis under native conditions and the protein that decolorized the azo dye (Methyl Red) with both NADH and NADPH was identified by mass spectrometry to be AzoA. Previously, the heterologously expressed and purified AzoA was shown to utilize NADH only for the reduction of Methyl Red. However, AzoA purified from the wild-type organism was shown to utilize both coenzymes but with more than 180-fold preference for NADH over NADPH as an electron donor to reduce Methyl Red. Also, its specific activity was more than 150-fold higher than the previous study on AzoAwhen NADH was used as the electron donor. The catalytic efficiency for Methyl Red reduction by AzoA from E. faecalis was several orders of magnitude higher than other azoreductases that were purified from a heterologous source.     

Helix → β conformational transition of poly(L-lysine) on dye binding

Binding of an azo dye, 4′-dimethyl amino azo benzene-4-carboxylic acid (DAAC) to poly(L -lysine) (PLL) in basic aqueous solutions at 20°C has been studied. The azo dye was found to bind to PLL when its side-chain amino groups are in the uncharged state. This was found to be a cooperative phenomenon, and the binding constant and cooperativity factor have been evaluated. The binding of the dye was found to result in a conformational transition of PLL from the α-helix to the β-sheet, which in turn helps in increased dye binding.